UK light heavyweight Joshua Buatsi secured a victory yet disappointing debut to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a close 10-round bout at the Manchester venue.
But Parker found success, connecting with powerful single shots in a fight where the styles failed to mesh, with constant grabbing spoiling the fight.
The scoring judges scored it 96-94 to Buatsi, with the final judge a 95-95.
"It wasn't my greatest showing but how do champions respond? They succeed," Buatsi stated in the ringside as he was faced disapproval from the spectators.
The Londoner got back to winning after his first professional defeat - an memorable fight with Callum Smith in February - to earn a 20th career victory.
Various analysts thought the challenger, thirty-one, should have been awarded the decision but the Derbyshire fighter suffered the second setback of his 28-fight professional journey.
The Champion Earns Win in Dull Encounter
Buatsi's progress has stalled in the past few years through contract problems and extended periods of inactivity.
Previously predicted as the rising talent of UK boxing, he now finds himself trying to realize his potential - perhaps in what appears to be a ultimate opportunity - under recent support.
He began cautiously, with neither fighter willing to overcommit in a calculated initial rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after suffering a hand injury in the contest, was making just his second appearance at light heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for the favorite, who utilized a protective stance to barely take the cleaner stanzas.
The spectators' acceptance wore thin amid regular grabbing, with the challenger slipping to the canvas various instances during close exchanges.
Parker ended stronger, but several stanzas were difficult to score. Nevertheless, former world champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the caliber of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Tribute Inspires Local Rivalry Fight
In the supporting bout, Lyndon Arthur beat Bradley Rea by divided decision in a terrific Manchester vs Manchester fight to capture the European light-heavyweight title.
The stadium fell silent for a deeply poignant homage before the fight as a bell ceremony sounded in memory of Manchester's own Ricky Hatton, who passed away aged 46 in last month.
It was the premier televised fight night in the location since Hatton's death. As the concluding sound disappeared, the quiet gave way to a roar of "there's just one Ricky Hatton".
The fighting during the bout matched the sentiment. The eventual winner was floored by a powerful punch flush on the jaw in the initial stage, getting up unsteadily to his footing on the referee's count.
But the traditional red equipment of the fighter soon came forward again. Across the ring, Rea - in rival City blue - was injured quickly, noticeable damage forming under his orbital area as the duo traded hard punches.
The challenger, 27, delivered effective strikes but Arthur, 34, fought fire with fire with stinging uppercuts as the action seldom decreased over the full distance.
Arthur narrowly won the result with scoring tallies of draw, 115-113 and 115-112, but each competitor were persistent and courageous, everything their hero the legend stood for.
